Process for producing a borax solution

ABSTRACT

A PROCESS FOR THE PRODUCTION OF AQUEOUS SOLUTIONS OF BORAX WHICH CAN BE DIRECTLY USED TO CRYSTALLIZE PENTA-AND/ OR DECAHYDRATED BORAX. USED ARE A SOURCE OF ALKALINE NA2O IN THE FORM OF HYDROXIDE, CARBONATE AND/OR BICARBONATE OF SODIUM, AND CLEAR AQUEOUS SOLUTIONS OF AMMONIUM BORATE WHICH ARE PRODUCED BY TREATING BORON AND CALCIUM MINERALS WITH AMMONIA AND CARBON DIOXIDE. THESE SOLUTIONS ARE INTRODUCED IN A DISTILLATION COLUMN WHERE THE AMMONIUM BORATES ARE DECOMPOSED UNDER HEAT TO PRODUCE A SOLUTION WHICH IS PRACTICALLY FREE OF AMMONIA. FOR THIS PURPOSE, THERE ARE SUCCESSIVELY INTRODUCED IN THIS COLUMN: THE CLEAR AQUEOUS SOLUTION OF AMMONIUM BORATES AT LEAST 50% OF THE QUANTITY OF ALKALINE NA2O WHICH IS STOICHIOMETRICALLY REQUIRED TO CONVERTYTHE AMMONIUM BORATES INTO BORAX. THE REMAINING PORTION OF ALKALINE NA2O WHICH IS STOICHIOMETRICALLY REQUIRED IS THEREAFTER INTRODUCED IN THE FORM OF SODIUM HYDROXIDE INTO THE SOLUTION WHICH HAS BEEN COLLECTED AT THE BOTTOM OF THE COLUMN. IN THIS MANNER THERE IS OBTAINED AN AQUEOUS SOLUTION OF BORAX WHICH CAN DIRECTLY BE USED TO CRYSTALLIZE PENTA-ANE/OR DECAHYDRATED BORAX BY ANY KNOWN MEANS. BY STOICHIOMETRIC QUANTITY OF ALKALINE NA2O IS MEANT 1 MOLE OF NA2O PER 2 MOLES OF B2O3, I.E. THE COMPOSITION OF BORAX: NA2O.2B2O3 OR NA2B4O7.

PROCESS FOR PRODUCING A BORAX SOLUTION Filed April 14, 1971 INVENTORSMarcel Casi in Paul Demi lie ATTORNEYS United States Patent O ItalyFiled Apr. 14, 1971, Ser. No. 133,827 Claims priority, applicationBelgium, Apr. 21, 1970,

8,039 Int. Cl. C01b 15/12, 35/00 US. Cl. 423280 3 Claims ABSTRACT OF THEDISCLOSURE A process for the production of aqueous solutions of boraxwhich can be directly used to crystallize penta-and/ or decahydratedborax. Used are a source of alkaline Na O in the form of hydroxide,carbonate and/or bicarbonate of sodium, and clear aqueous solutions ofammonium borate which are produced by treating boron and calciumminerals with ammonia and carbon dioxide. These solutions are introducedin a distillation column where the ammonium borates are decomposed underheat to produce a solution which is practically free of ammonia. Forthis purpose, there are successively introduced in this column:

the clear aqueous solution of ammonium borates at least 50% of thequantity of alkaline Na O which is stoichiometrically required toconvert the am monium borates into borax. The remaining portion ofalkaline Na O which is stoichiometrically required is thereafterintroduced in the form of sodium hydroxide into the solution which hasbeen collected at the bottom of the column. In this manner there isobtained an aqueous solution of borax which can directly be used tocrystallize penta-and/or decahydrated borax by any known means. Bystoichiometric quantity of alkaline Na O is meant 1 mole of Na O per 2moles of B i.e. the composition of borax: Na O-2B O or Na B O BACKGROUNDOF THE INVENTION The present invention relates to a process forconverting into aqueous solutions of borax, the clear aqueous solutionsof ammonium borates which are obtained when treating minerals of boronand calcium with ammonia and CO2.

These aqueous solutions of ammonium borates are a well knownintermediate used on an industrial basis to produce borax and boricacid. They contain unreacted ammonium carbonate.

It is known that it is possible to convert these ammonium boratesolutions into borax by adding sodium chloride as proposed in SwissPatent No. 341,803, filed May 13, 1959, in the name of Enrico Asseo.There is obtained in this manner an aqueous solution from which a boraxcan be crystallized by cooling and adjustment of the pH with ammonia. Inorder to satisfactorily operate this process on an industrial basis, theammonia which is used at the start must be recovered. However ammoniaremains combined in solution in the form of ammonium chloride andconsequently there must be provided an additional plant for separatingand decomposing ammonium chloride.

A much more simple way to treat ammonium borate solutions is to heat anddecompose for directly evolving ammonia and CO and to concentrate theresulting solutions in order to finally obtain a boric acid solutionwhich is practically free of ammonia and CO Such a process is describedin German Pat. No. 1,217,933, filed May 10, 1960, in the name ofLarderello. This process enables the direct recovery of ammonia and COwhich can thereafter be recycled to treat the mineral. To obtain borax,caustic soda or sodium carbonate could be added to the solution of boricacid as it is suggested in German Pat. No. 71,310, filed June 14, 1892,in the name of Chemische Fabrik Bettenhausen. However, in the lattercase, the solution which is obtained contains CO This series ofoperations is however too complicated to be carried out on an industrialbasis. Furthermore, there must be provided special equipment, forexample one which is made of stainless steel, and which is resistant toboric acid solutions when the latter are heated to a temperature highenough to decompose ammonium borate.

SUMMARY OF THE INVENTION An object of the present invention, therefore,is to overcome the disadvantages of the processes aforementioned.

It is another object of the present invention to provide a simple andeflicient means to directly convert, in a single step, aqueous solutionsof ammonium borates into aqueous solutions of borax practically free ofammonia, the latter being recovered and capable of being used again totreat the mineral.

These as well as other objects which will become apparent in thediscussion that follows are achieved, according to the presentinvention, by a process for the production of aqueous solutions of boraxwhich can be directly used to crystallize penta-and/or decahydratedborax. Such solutions are obtained from a source of alkaline Na O in theform of hydroxide, carbonate and/ or bicarbonate of sodium, and clearaqueous solutions of ammonium borate which are produced by treatingboron and calcium minerals with ammonia and carbon dioxide. The boratesolutions are introduced into a distillation column where the ammoniumborates are decomposed under heat to produce a solution which ispractically free of ammonia. For this purpose, there are successivelyintroduced into this column:

(1) The clear aqueous solution of ammonium borates, and

(2) At least 50% of the quantity of alkaline Na O which isstoichiometrically required to convert the ammonium borates into borax.

The remaining portion of alkaline Na O which is stoichiometricallyrequired is thereafter introduced in the form of sodium hydroxide intothe solution which has been collected at the bottom of the column. Inthis manner there is obtained an aqueous solution of borax which candirectly be used to crystallize penta-and/or decahydrated borax by anymeans known per se.

By stoichiometric quantity of alkaline Na O is meant 1 mole of Na O per2 moles of B 0 i.e. the composition of borax: Na -O-2B O or Na B O BRIEFDESCRIPTION OF THE DRAWING The sole figure of the drawings is a processschematic illustrating the process of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS It will be noted that the Na Owhich is introduced in the column causes an easier decomposition ofammonium borates. In addition there results a decreased vaporconsumption and a lowering of the pressure and of the operatingtemperature in the column. Furthermore, it is no longer required to havea column completely made of stainless steel.

In accordance with the invention, it is even possible to use a columnwhich is entirely made of ordinary steel, provided the alkaline Na O ismixed at least in part with the solution of ammonium borates before thelatter is introduced into the column.

. It is also possible to devise a column in which the upper portion ismade of stainless steel and the lower portion is constructed of ordinarysteel. The introduction of alkaline Na O is effected at the bottom partof the stainless steel portion.

It is therefore possible according to the invention to introduce theentire portion of alkaline Na O which is stoichiometrically required inthe column, without meeting serious corrosion problems with ordinarysteel. A borax solution which is free of the initial ammonia isretrieved at the foot of the column, which solution can easily be usedto crystallize decahydrated borax.

If it is intended to pursue the crystallization until pentahydratedborax is obtained, certain difficulties will be met due to the presenceof CO in the solution which exits from the column. Purges by withdrawinga part of the mother liquors must be carried out to limit the content ofCO in the mother liquor used for the crystallization of pentahydratedborax to 20 g. Co /kg. of solution.

To overcome this disadvantage, it is possible, in accordance with theinvention, to introduce in the column a fraction only of the requiredN320, the remaining portion of Na O being introduced at the bottom ofthe column in the form of NaOH.

In this manner, the following results have been obtained starting froman initial solution which contains at the input of the column:

B 100 g./kg. of solution NH 30 g./kg. of solution CO 20' g./kg. ofsolution to which there are added the following quantities of N320.

In practice, it will be realized that the crystallization ofpentahydrated borax is not disturbed when the CO content at the bottomof the column remains lower than 3 g./kg. of solution. Preferably, thequantity of Na O which is introduced in the column is therefore limitedto at most 82% of the entire quantity.

In this manner, for the same quantity of borax which is produced, it ispossible while working under the conditions No. 2 to save about to ofcaustic soda not counting the gains in B 0 which is lost duringpurgingwhen operating under conditions No. 1, i.e. when Na O iscompletely introduced in the column.

However, it will be observed that when introducing less and lessalkaline Na O in the column, the ordinary steel of the column has anincreasing tendency to become corroded, especially at a temperaturehigher than 100 C.

At 100 C., the quantity of Na 0 which is introduced can vary at willbetween 50 and 100% of the total charge, and there is practically nocorrosion of the ordinary steel.

On the other hand, at 105 C., the speed of corrosion of the ordinarysteel remains low (lower than 1 g./m. day) as long as there isintroduced at least 75% NagO in the column. However, corrosion increasesrapidly when introducing less Na O.

-In order to prevent using corrosion inhibitors or stainless steel, andto facilitate to the maximum the decomposition of ammonium borate whilerecovering a minimum amount of CO at the bottom of the column, it isrecomm nded, in accordance with the invention, to

introduce in the column not less than half the required amount of N320.

To prevent an accumulation of CO in the crystallization cycle, it isalso interesting to charge the crystallization mother liquors with thesolution of ammonium borates to the head of the column.

In this case, it is obviously required to take into account the quantityof Na O which is brought in the mother liquors in order to calculate thequantity of N320 to be introduced in the column. This operation enablesa decrease in the purgings of the mother liquors.

The solutions of borate which are obtained in accordance with theinvention can then be used directly for the crystallization ofdeca-and/or pentahydrated borates by any means known per se.

Further illustrative of the present invention is the following example:

Referring to the sole figure of the drawing, a clear aqueous solution ofammonium borates is introduced through pipeline 1 into continuouslyoperatnig mixer 2 The composition of this aqueous solution is asfollows:

G./kg. B203 100 NH3 as so co 20 Additionally introduced into mixer 2through chute 3 is powdered sodium carbonate in suflicient quantity toprovide a Na O concentration of 33 grams per kilogram of originalsolution or of the Na O with respect to the stoichiornetry of borax. Theresulting solution is continuously charged at a temperature of C. todistillation column 4 through pipeline 5. The distillation columncontains 40 bubblecap trays, the solution being charged at the 1st trayfrom the top. The length of the column is 6 meters. The steel used forconstruction of column 4 had the following composition: 0.2. 0wt.-percent C., 0.50 wt.-percent Mn, remainder Fe. The composition ofthe vapor obtained through pipeline '6 is as follows, on a weight basis:

Percent NH 3.7 00 5.2 H 0 91.1

The temperature of this vapor is 100 C. The liquid leaving throughpipeline 7 at C. and flowing into mixer 8 has the following composition:

G./ kg. 2 3 1 0O N320 m CO 2 Vessel 9 contains a 50% solution of NaOH,which is fed through pipeline 10 to mixer 8 in sufiicient quantity toprovide a solution having the stoichiometry of borax.

The resulting solution which has the following composition:

G./kg. B 0 97 Na O 43 .5 CO 2 Pipeline /pipeline 5:0.77 Pipeline Jg/pipeline 5 =0.83 l yeline Ylp p 5 1 The pressure in the column 4 wasatmospheric.

The column 4 was observed to corrode at a speed of only about 0.5 g./m.day.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

We claim:

I. A process for the production of borax, comprising the steps ofcharging an ordinary-steel distillation column with a clear aqueoussolution containing B and NH and with at least 50%, and up to 100%, ofthe quantity of alkaline Na O in the form of at least one materialselected from the group consisting of the hydroxide, carbonate, andbicarbonate of sodium which would be required to convert all the B 0 toNa O-2B O operating the distillation column for removing NH to yield anaqueous solution free of NI-I at the bottom of the column, adding to thesolution obtained at the botom of the column any additional Na O, in theform of sodium hydroxide, needed for converting all of the B 0 to andcrystallizing from the resulting NH-free, Na O-ZB O solution a boraxselected from the group consisting of decaand pentahydrated borax.

2. A process as claimed in claim 1, further comprising the step ofcharging mother liquors, which remain after the step of crystallizing,to the head of the distillation column.

3. A process for the production of borax, comprising the steps ofcharging an ordinary-steel distillation column with a clear aqueoussolution containing B 0 and NH, and with at least and at most 82%, ofthe quantity of alkaline Na O in the form of at least one materialselected from the group consisting of the hydroxide, carbonate, andbicarbonate of sodium which would be required to convert all the B 0 toNa O-2B O operating the distillation column for removing NH to yield anaqueous solution tree of NH at the bottom of the column, adding to thesolution obtained at the bottom of the column sufficient additional NaO, in the form of sodium hydroxide, that all of the B 0 is converted toand crystallizing from the solution resulting from the step of adding ahorax selected from the group consisting of decaand pentahydrated borax,in which process the crystallizing is not disturbed by the presence ofCO in the solution yielded at the bottom of the column.

References Cited UNITED STATES PATENTS 1,450,975 4/1923 Kelly 23592,867,502 1/1959 Stange et al. 23-59 3,018,163 1/1962 May et al. 2359HERBERT T. CARTER, Primary Examiner US. Cl. X.R. 203-33. 36. 37

